We took our boat out yesterday in 40 degree water, and had what I think is an extremely unusual issue. Thankfully, our local boat mechanic and dealarship owner were on board to watch these hard core "fools" surf this late in the year.

I must prefact this by saying how much I trust my local boat dealer and mechanic. As luck would have it, they were both on my boat when we had this issue.

Launched the boat in 40 degree water. Idled out into the lake and filled the sacks. Put on the drysuit and started surfing. All this took about a little over 45 minutes... and the boat idled the entire time.

Set cruise at 10.4mph and started surfing. 45 seconed in the first pass, a solid alarm sounded, smart tow disengaged and speed reduced to idle. Alarm quit. Guardian would NOT define any issues. Mechanic checked a couple things out and we attemped a second pass. Same result. We've had issues with smart tow in speed mode historically, so we switched it up to rpm mode... identical results on two more passes. We then disengaged smart tow and attempted cruising speed. Same results after 45 seconds. We "limped" back to the dock where the mechanic investigated even more. Only thing he noticed that was out of the ordinary was the manifolds were incredibly "cool" to the touch.

Loaded up and returned to the dealership. Mechanic hooked up the laptop... and said the codes were "wierd"... had to call Merc Monday AM.

I went out to the shop Monday afternoon to see what was up... and the mechanic has this big smile on his face. He ran the boat in the shop, and everything was perfect. He had called Merc and the "just laughed and said WINTERIZE THE BOAT. The water's just too cold for the engine to warm up".

OK... so my window of use in Wyoming just got smaller? Dealer "speculated" that had we initially "gotten on" the throttle for a while, the engine would have achieved enough heat to run.

Still doesn't make me feel any better. I mean... although there aren't many, certainly there are inboard boats that are run this time of year in Montana... North Dakota... Michigan... Canada?

PCM had something like that also where one of the cats heated up to 130 and the other would only reach 90 when in 50 degree water, they (PCM) developed a new system to route hoses to where both cats would reach 130 at the same time.

That is odd. Hope they work that out for you. To me the right answer wouldn't be "just winterize your boat". We didn't run late this fall because of switching boats and a few kid activities, but we will be going early in the spring. We can get 70 degree days now and then right after the ice goes out. So Hopefully PCM has theirs worked out as thats whats in my boat.

Well, you could go to a closed loop cooling modification. The easiest would be to just run the boat up to speed for a bit before you put the wakesurfing load on it. I'm quite sure that would solve the problem. I don't think that 40° water is too cold. 32° is too cold but you can tell by how hard it is to chip out the thermometer.

That seems pretty ridiculous..... We hit the water every spring here in Minnesota on ice-out. The water is almost always 37 degrees that day. I've never had an issue like that. Old boat was a 98 Supra Comp- PCM 350 with TBI injection. New boat is a 2010 Malbu Wakesetter VTX w/ Monsoon.

That seems pretty ridiculous..... We hit the water every spring here in Minnesota on ice-out. The water is almost always 37 degrees that day. I've never had an issue like that. Old boat was a 98 Supra Comp- PCM 350 with TBI injection. New boat is a 2010 Malbu Wakesetter VTX w/ Monsoon.

While I've had the same experience in cold water here in MN - the idea he is describing is plausible. Only because at idle, the cold water doesn't warm anything up. And without any spirited driving, when the ecu sees the large load (weighted, slow launch surfing) it will cause it to go into limp mode.

I've had this same thing happen in cars here in MN in the winter. It's 20 below, car sits. When you start it and dont' let it warm up enough, it goes into limp mode.

If he had done some spirited driving - then this would be odd. but if it just idled in very cold wateer with cold air temps, it seems plausible. The real test would be to try to replicate this scenario with cold water and some idling but then rev the motor in neutral quite a bit and pick up some speed, etc..

You have to think about the fact the engine is constantly getting 40 degree water pumped through it. So can it really warm up to a normal, or even safe operating temp in those conditions? Sound like with the sophisticated ECM system that the answer is no. May be a different story with a closed loop system with heat exchangers, but the exhaust would still have lake water circulating through it.

We are going surfing tomorrow here in MN, water is cold, I will update with our lack of issues.

That's not the point..

The point is to recreate his EXACT scenario with his same boat/ECM.. We have all went out and rode, surfed, boarded in sub 40 degree water.. If you idle your boat tomorrow for 45 minutes with no revving, then try to put a heavy load on it with ballast - your ECM may not be happy and go into limp mode.

It's about this particular scenario and the settings of the ECM on the manufacturer of his rig.. It's not about the cold water. We've all done that.

Not unless a boat thermostat works different than in a machine, car or anything else. Until it hits the temperature of the thermostat it shouldn't be letting lake water into the engine, not that much anyway, just the slight bypass. If it didn't control the flow chances are you'd never hit operating temp in 40 degree water. Thermostat has to do it's job to maintain and control the temp. Most of our boats have what they call an open system because they are open to the lake for cooling. They are still a thermostat flow controlled system. So at idle the engine is circulating the same 40 degree water which will warm up from the heat of the engine. Maybe not to operating temp, but it shouldn't be getting continuous flow of lake water if the thermostat is closed.

It does help it warm up faster by not letting the cold water in full flow or at all. Example my jeep thermostat was hanging open last year. In the winter it was fine at driving rpm, but when you slowed to an idle the temp would drop because the thermostat wouldn't close as the engine produced less heat. Now the exhaust is a different story because if it doesn't go into the block it's 40 degrees straight to the exhaust. But with water that cold even with closed thermostat restricted water flow it might still be to cold to maintain temp at idle.

I was a mechanic for 7 year at Ziegler before I retrained. You said he is just cycling sub 40 degree water..which is wrong and not what I said. If the thermostat is closed there shouldn't be sub 40 degree water coming into the block. The water that started at 40 should be warming. But I am probably wrong there too I suppose.

Slap a carb on it and call it a day. My old junk works fine with water in the 40s every season, temps around 140-150 and plenty of heat in the raw water because there's warm air coming from the heater core.

I was a mechanic for 7 year at Ziegler before I retrained. You said he is just cycling sub 40 degree water..which is wrong and not what I said. If the thermostat is closed there shouldn't be sub 40 degree water coming into the block. The water that started at 40 should be warming. But I am probably wrong there too I suppose.

IIRC, these CAT engines have temp sensors in the risers. So, depending on how the ECM is programmed, there may be a limp for when the temp differential exceeds a certain threshold. So, the waters-too-cold theory could be plausible. reason being, is that with the thermostat closed, cold lake water will bypass the block and circulate through the exhaust, so that they are always getting cooled.

Any chance you'll be on Pulaski Casey?? I think I've seen a Marine Max truck at the launch before.... If you see someone standing on shore waving a Sky Ski come pick me up!! I live 4 houses down from the launch...

iirc, these cat engines have temp sensors in the risers. So, depending on how the ecm is programmed, there may be a limp for when the temp differential exceeds a certain threshold. So, the waters-too-cold theory could be plausible. Reason being, is that with the thermostat closed, cold lake water will bypass the block and circulate through the exhaust, so that they are always getting cooled.

John notes that the alarm occurred 45 sec into the first surf run. Do you think its possible that the boat was able to reach 10.4 in that time? I do, since he also noted that the Smart Tow disengaged. Sounds like the boat did indeed reach 10.4 as the Smart Tow was engaged

Although an engine will reach operating temp faster when above idle, it will reach operating temp when left to just idle. Feel free to experiment with your own boat next time out on a cold day.

I have offered a technical explanation as to why I believe the theory is plausible. Would you please offer more as to why its impossible? A little more perhaps than you launching your boat in cold water and not experiencing an issue. Im curious to hear more. What engine year, make and model does you boat have?

John notes that the alarm occurred 45 sec into the first surf run. Do you think its possible that the boat was able to reach 10.4 in that time? I do, since he also noted that the Smart Tow disengaged. Sounds like the boat did indeed reach 10.4 as the Smart Tow was engaged

Although an engine will reach operating temp faster when above idle, it will reach operating temp when left to just idle. Feel free to experiment with your own boat next time out on a cold day.

I have offered a technical explanation as to why I believe the theory is plausible. Would you please offer more as to why its impossible? A little more perhaps than you launching your boat in cold water and not experiencing an issue. Im curious to hear more. What engine year, make and model does you boat have?

I was being sarcastic..

I think you are right... What's odd is that the ECM/Guardian didn't throw any codes.. It should have given an error code for the sensor saying it wasn't up to operating temperature.

I've ha this scenario happen in my wifes Volvo S60. Ultra cold weather start + an attempt to run will put it into limp mode.. It will idle all day but unless it starts to see some load (even neutral RPM increase) - it will start to warm and the ECM will allow it to run.

Will all boats reach operating temp idling regardless of water temp, cooling system and sensors it is equipped with? I dont' know that.. I was saying that the mechanic and Mecrcruisers opinion seems logical.. So does yours. The only part that doesn't add up is no code thrown. I would think it would throw a code when it went into limp mode..

Sorry about the sarcasm.. I'm sarcastic to a fault.. I don't think this is black/white and it would be hard to replicate the exact scenario. I've ran many of my boats and friends boats in colder water/air combinations - but unless you replicated the length of idle, water temp, the load/ballast, the launch and then that boats ECM settings - it's a lot of guess work which SHOULD have been taken care of with a code reader.

No worries JD, I missed the sarcasm. I do agree that the lack of a code is odd. Logic would dictate that if a condition occurred that resulted in reduced-power/limp-mode operation, I would expect a code to be present. John did sate that codes were set, but did not list them. The tech stated that they were "weird". Id bet that the code was for an exhaust temp out of limits and the tech was thinking it was set for being too hot. With water temps at 40, that would be weird, but if the ECM is also comparing the two sensors, if the split was far enough, irrelevant to their actual temp, this could be why it went in to limp-mode.

Id love to know what codes where set and the criteria required to set them.

Again, no worries, rereading with a little tongue'n check, its makes sense

Will all boats reach operating temp idling regardless of water temp, cooling system and sensors it is equipped with? I dont' know that..

Every marine cooling system I'm aware of will get the engine to operating temp regardless of water temp. Manifolds will run cooler though, as with colder water the thermostat is closed more often and less hot water from the engine is discharged through the manifolds and risers, so more raw unheated water will run through the exhaust components than if the water temp is warmer and the thermostat stays open more often. Thus more 40* raw water is going through the exhaust than 145*-180* preheated water from the engine... More cooling to the exhaust.

An engine may not reach operating temp is if it the thermostat is not present or has failed open. Before the water is cold enough that you're coming nowhere near operating temp, it would no longer be water.

The only other way an engine may not reach full operating temp is if a high flow thermostat is used or one with a fairly large bleed/relief/bypass hole.

No worries JD, I missed the sarcasm. I do agree that the lack of a code is odd. Logic would dictate that if a condition occurred that resulted in reduced-power/limp-mode operation, I would expect a code to be present. John did sate that codes were set, but did not list them. The tech stated that they were "weird". Id bet that the code was for an exhaust temp out of limits and the tech was thinking it was set for being too hot. With water temps at 40, that would be weird, but if the ECM is also comparing the two sensors, if the split was far enough, irrelevant to their actual temp, this could be why it went in to limp-mode.

Id love to know what codes where set and the criteria required to set them.

Again, no worries, rereading with a little tongue'n check, its makes sense

The boat did achieve 10.4... and 45 seconds before the Guardian reduced to limp mode was an estimate. Could have been a minute, but not more than that. Additionally, we disenaged the speed control and achieved 25mph for 45 sec - 1 min before being reduced to limp mode. My mechanic is out of town until next Tuesday... and I'm headed out of the country for a couple weeks on Monday. I'll try to contact him to find out what the exact codes were before I "head south".

Depending on if it has a heater, or how its hooked into the cooling system, the water going thru the heater core will be by passing the thermostat and possibly allow the engine to get more cold sea water and not heat up. Ok heat when idling and water flow is low, but give it some throttle and more water flow and it cools the engine. My bet is tho, that it has something to do with low O2 temps kicking the ECM into open loop and causing it to go into limp mode.

We went out and got on last wakeboard set in. As you can see in the pi , the water is cold, and unfortunately the air temp didn't make it as high as expected over here in the West Metro. Still a ton of fun. Was able to with stand about 6 or 7 falls, until the last one in which I went in head first....at 45 deg water feels more like a door.

No problems with the cold water and the engine. Running a PCM ZR450 in the G23.